Protection from Aortic Aneurysm by Bmal1 deletion from Smooth Muscle Cells Recognized as an important cause of death in the aging population, aortic aneurysm is a disease that is currently treated only through surgery. Therefore, a thorough understanding of the molecular mechanism of aortic aneurysm is a pressing matter. Bmal1 is a basic helix loop helix (bHLH) transcription factor and is an indispensable core clock gene. Bmal1 is expressed in vascular smooth muscle but its function remains mostly unknown.The current study is designed to test a potential role of Bmal1 in aortic aneurysm. Our preliminary data have shown that deletion of Bmal1 from smooth muscle cells has been protective from DOCA plus salt induced aortic aneurysm formation in 8 to 9 months old mice. This protection is independent of increase in blood pressure. We have also found that smooth muscle specific knockout mice have an increase of Tissue inhibitor of mellaproteinases 4(TIMP4) at basal level and a further increase in TIMP4 after DOCA plus salt with no gelatinases activities. TIMP4 is the fourth member of endogenous inhibitors of matrix metalloproteinases (MMPs). TIMP4 expression is restricted to cardiovascular tissues and has been shown to be a strong inhibitor of MMP2. TIMP4 role in aortic aneurysm formation is unknown. MMPs are proteases that degrade component of the extracellular matrix (ECM). Many MMPs have been identified and classified depending on their substrates. An imbalance between MMPs and TIMPs has been shown to be a major cause of vascular diseases such as aortic aneurysm. Gelatinases MMP2 and MMP9 have been shown to be upregulated in patients with aortic aneurysm. Our hypothesis has been that Bmal1 regulates TIMP4 expression therefore, playing a role in aneurysm formation. To test this hypothesis, we have constructed two specific aims: 1) to test the hypothesis that deletion of Bmal1 in smooth muscle cells will protect from other model of aortic aneurysm such as angiotensin II and CaPO4 through TIMP4 upregulation. 2) To test the hypothesis that upregulation of TIMP4 mediates the protective effect observed in SMC-Bmal1 KO mice. To determine whether SMC-Bmal1 KO mice will be protected from other models of aortic aneurysm, we will first induced aortic aneurysm using AngII+salt then compare the relative aortic aneurysm incidence. Second, we will induce aortic aneurysm using CaPO4 in SMC-Bmal1 KO mice. To look at the role of TIMP4 in aortic aneurysm, we will use TIMP4 KO mice and TIMP4-Bmal1 KO mice and induce aortic aneurysm using the DOCA plus salt model which we will then compare the incidence of aortic aneurysm. We will use different staining to distinguish the pathology among the different mice that will be used. The results from this proposed study will provide new insights to the molecular mechanisms underlying aortic aneurysm, and may lead to a new therapeutic target for the aortic aneurysm treatment.